1. Field of the Invention
The present invention relates to a combustion-operated setting tool for driving in fastening elements, and including a guide cylinder, a setting piston displaceable in the guide cylinder, a combustion chamber defining a combustion chamber axis and having a first end adjacent to the guide cylinder and a second end spaced from the guide cylinder; a fuel inlet opening into the combustion chamber for feeding fuel therein and located at the first end of the combustion chamber, an ignition element for igniting the fuel in the combustion chamber, and a ventilator supported on a rear wall of the combustion chamber at the second end of the combustion chamber.
2. Description of the Prior Art
The setting tools of the type described above can operate, e.g., with gaseous or liquid vaporizable fuels. During a setting process, the setting piston is driven by expanding combustion gases for driving a fastening element in a workpiece. Before start of the combustion process, fuel is injected in the combustion chamber and is mixed with air that fills the combustion chamber by a ventilator or impeller. Simultaneously, the turbulence, which is necessary for combustion, is produced. After the combustion process, the ventilator blows out the combustion products from the combustion chamber and aspirates fresh air in. For cooling the power tool, the ventilator is operated after rinsing of the combustion chamber and is turned off after a predetermined time period. The ventilator is driven by a motor, preferably, electric motor. The ignition of the air-fuel mixture that fills the combustion chamber is effected with an ignition device that includes, e.g., a spark plug.
European Publication EP 1 693 158 A1 discloses a combustion-operated setting tool of the type discussed above and including a combustion chamber and a ventilator located therein. The ventilator is driven by a motor which is supported in a recess in a combustion chamber rear wall that is formed as a cylinder head. A fuel inlet, which opens into the combustion chamber extends through the cylinder head. The fuel inlet is connected with a fuel source by a fuel conduit. An ignition element of an ignition device and which is formed as a spark plug likewise is arranged on the cylinder head. Both the fuel inlet and the spark plug, which are located in the combustion chamber, are, thus, located behind the ventilator in the flow direction of the flow produced by the ventilator.
The drawback of having the fuel inlet and the ignition element located behind the ventilator (at the rear wall) consists in that the ignition of the air-fuel mixture is only then possible when the fuel, which was injected in the combustion chamber, has been uniformly turbulently distributed to a most possible extent. The user, in order to insure a reliable ignition, should, therefore, actuate the trigger switch, which actuates ignition, only after a certain time delay after injection of the fuel in the combustion chamber (usually, the injection is initiated by the setting tool being pressed against a workpiece). This necessary delay period can be perceived by the user as troublesome. When the injection of fuel is initiated by the setting tool being pressed against a workpiece, then pressing and actuation of the trigger switch simultaneously or immediately after the press-on movement of the setting tool would lead to disturbances or even failures of the ignition.
Accordingly, an object of the present invention is to provide a combustion-operated setting tool of the type described above in which it is possible to set a fastening element disturbance-free and with a sufficient drive energy already after a minimal delay period between the injection of fuel in the combustion chamber or pressure of the setting tool against a workpiece and actuation of the setting process by the trigger switch.